I propose to investigate three kinds of interaction that occur between the different classes of retinal receptor: (1) Information about quantum absorptions in the three photopigments is transformed and transmitted as two opponent (chromatic) and one luminance (achromatic) signal. Analysis of the physiological work suggests that for sufficiently high contrasts both of these channels enhance contours, but that for low luminance contrasts, chromatic contrasts are not enhanced. I will attempt to determine psychophysically the separate responses of the chromatic and achromatic systems to high and low contrast edges by taking advantage of the lower fusion frequency of the chromatic channels, and by measuring the sensitivity to minimum-border chromatic increments, rather than luminance increments, across various contours. (2) Physiological analyses of the retina have shown interactions between rods and cones. Our past work, while showing substantial interaction between rods and cones, indicates a different site for the interaction than shown by some, but not all, of the physiological work. I propose to get more complete data on the suppressive effects of cones upon rods for both forward and backward masking situations. We have also shown that rods can selectively alter the sensitivity of the cone luminance channel for transient conditions. Evidence for a sustained effect is of great importance for determining the origin of these effects. (3) We have identified a linking interaction between some classes of receptor, which is controlled by, as far as we know at present time, the amount of white-light adaptation. I will attempt to determine a possible spectral sensitivity for the different kinds of linking by using chromatic adaptation.